1. Field of the Invention
This invention relates to a master cylinder having a quick-fill function as the result of movement of a piston in a stepped bore. A resiliently positioned ball located in a unitary structure allows fluid to escape from the quick-fill chamber to limit the fluid pressure level therein. Should the escape of fluid be delayed, the unitary structure moves to provide an additional flow path for the communication of fluid from the quick-fill chamber.
2. Description of the Prior Art
Master cylinders having a quick-fill function are capable of delivering a large quantity of working fluid to a system during the initial stage of the operating stroke thereof, while producing a high pressure in the latter stage of the working stroke thereof. Master cylinders of this type includes a cylinder having a stepped bore and a stepped piston slidably fitted in the stepped bore of the cylinder. The piston and cylinder jointly forming a first pressure chamber within the large diameter of the bore and a second pressure chamber within the small diameter of the bore. The first pressure chamber communicates with a reservoir through a check valve which allows flow of the working fluid from the reservoir to the first chamber when a negative pressure is effective in the first pressure chamber and through a relief valve which allows flow of the working fluid from the first pressure chamber into the reservoir when the pressure effective within the first chamber exceeds a predetermined pressure. The master cylinder is adapted to allow flow of the working fluid from the first pressure chamber into the second pressure chamber through the periphery of a cup seal attached to the piston section of a small diameter of the stepped piston due to the pressure difference between the pressure of the first and second pressure chambers. U.S. Pat. Nos. 4,571,944; 4,694,651 and 4,702,077 are illustrations of master cylinders that incorporate this type of quick-fill function.
It is known that the quick-fill chamber needs to be opened to the reservoir when a predetermined fluid pressure level is achieved in the quick-fill chamber. However, on fast or spike applications the release of fluid from the quick-fill chamber is restricted and as a result more fluid pressure than desired is developed in the quick-fill chamber which reduces the energy transmitted to the main chamber with an end result reducing the operational fluid pressure supplied to the wheel brakes.